Process for converting carbon dioxide to oxygenates

ABSTRACT

A catalyst and process for converting carbon dioxide into oxygenates. The catalyst comprises copper, zinc, aluminum, gallium, and a solid acid.

RELATED APPLICATIONS

[0001] This is a continuation of application Ser. No. 09/963,831, filedSep. 26, 2001, entitled CATALYST FOR CONVERTING CARBON DIOXIDE TOOXYGENATES AND PROCESSES THEREFORE AND THEREWITH, and herebyincorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to the conversion ofcarbon dioxide to oxygenates. In another aspect, the invention concernsa catalyst for converting a feed comprising carbon dioxide and hydrogeninto methanol and dimethyl ether.

[0004] 2. Discussion of Prior Art

[0005] Carbon dioxide for industrial use is typically recovered fromsynthesis gas production, substitute-natural gas production, cracking ofhydrocarbons, and natural springs or wells. Although carbon dioxide canbe used for numerous purposes such as, for example, refrigeration,carbonating beverages, and as an aerosol propellent, in certainsituations it may be more desirable to convert carbon dioxide to otherhigher-value compounds such as oxygenates.

[0006] Oxygenates can be used for a variety of purposes such as, forexample, enhancing of motor fuel octane and improving the emissionsquality of motor fuel. Methanol and dimethyl ether are two oxygenateswhich can be of particularly high value. Methanol can be used for avariety of purposes including, for example, as an alternative motorfuel, as an intermediate in the production of high octane ethers (e.g.,MTBE), and as a fuel for fuel cell driven vehicles. Dimethyl ether isalso useful for a variety of purposes including, for example, as analternative motor fuel, as a starting material towards the synthesis ofvarious hydrocarbons, as a fuel additive to lower emissions, and as anaerosol propellent.

[0007] Although it is known that synthesis gas comprising carbonmonoxide, carbon dioxide, and hydrogen can be converted into oxygenatesusing a copper-containing catalyst, there exists a need for a catalystwhich is effective to convert carbon dioxide into oxygenates withincreased carbon dioxide conversion as well as increased productselectivity towards methanol and dimethyl ether, particularly dimethylether.

OBJECTS AND SUMMARY OF THE INVENTION

[0008] An object of the present invention is to provide a catalyst andprocess for converting carbon dioxide to oxygenates wherein there is anincreased carbon dioxide conversion.

[0009] A further object of the present invention is to provide acatalyst and process for converting carbon dioxide to oxygenates whereinthere is an increased product selectivity towards methanol and dimethylether.

[0010] A still further object of the present invention is to provide acatalyst and process for converting carbon dioxide to oxygenates whereinthere is an enhanced product selectivity towards dimethyl ether versusmethanol.

[0011] An even further object of the present invention is to provide acatalyst and process for converting carbon dioxide to oxygenates whereinthe amount of carbon monoxide produced is minimized.

[0012] A yet further object of the present invention is to provide anovel process for preparing a catalyst effective to convert carbondioxide into oxygenates.

[0013] It should be noted that not all of the above-listed objects needbe accomplished by the invention claimed herein and other objects andadvantages of this invention will be apparent from the followingdescription of the invention and appended claims.

[0014] In accordance with one embodiment of the present invention, acatalyst composition is provided. The catalyst composition comprisescopper, zinc, aluminum, gallium, and a solid acid.

[0015] In accordance with another embodiment of the present invention acatalyst composition for converting carbon dioxide to methanol anddimethyl ether is provided. The catalyst composition comprisesreduced-valence copper, zinc oxide, aluminum oxide, gallium oxide, and azeolite having an acid function.

[0016] In accordance with another embodiment of the present invention, amethod of making a catalyst composition is provided. The methodcomprises the steps of: (a) combining a copper-containing compound, azinc-containing compound, an aluminum-containing compound, agallium-containing compound, and a solid acid compound to form acatalyst mixture; (b) calcining the catalyst mixture to form a calcinedcatalyst; and (c) reducing the calcined catalyst to form a reducedcatalyst.

[0017] In accordance with a still further embodiment of the presentinvention, a process for converting a carbon dioxide-containing feedinto oxygenates is provided. The process comprises the steps of: (a)contacting the carbon dioxide-containing feed with a catalystcomposition comprising copper, zinc, aluminum, gallium, and a solid acidin a reaction zone under reaction conditions sufficient to convert atleast a portion of the carbon dioxide-containing feed into oxygenates;and (b) recovering of at least a portion of the oxygenates from thereaction zone.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] In accordance with the first embodiment of the present inventiona catalyst comprising copper, zinc, aluminum, gallium, and a solid acidis provided.

[0019] The copper component of the inventive composition can exist inthe form of any copper-containing compound such as, for example,elemental copper, copper oxide, and/or a copper oxide precursor. It ispreferred for the inventive catalyst composition to contain from about 2to about 50 weight percent copper based on the total weight of thecatalyst composition, more preferably from about 10 to about 35 weightpercent copper, most preferably from 20 to 30 weight percent copper. Atleast a substantial portion of the copper component is preferablypresent in the inventive catalyst composition in a reduced-valencestate. The valence of the copper in the reduced-valence state (i.e., thereduced-valence copper) is less than the valence of copper in its commonoxidized state, preferably less than two, most preferably zero. It ispreferred that at least about 20 weight percent of the copper present inthe inventive catalyst composition be present in the reduced-valencestate, more preferably at least about 60 weight percent of the copper ispresent in the reduced-valence state, and most preferably at least 80weight percent of the copper is present in the reduced-valence state.

[0020] The zinc component can exist in the form of any zinc-containingcompound such as, for example, elemental zinc, zinc oxide, and/or a zincoxide precursor. Preferably, the zinc component comprises zinc oxide. Itis preferred for the inventive composition to contain from about 1 toabout 40 weight percent zinc based on the total weight of the catalystcomposition, more preferably from about 5 to about 30 weight percentzinc, most preferably from 10 to 20 weight percent zinc. The weightratio of zinc to copper in the inventive catalyst composition ispreferably from about 0.01:1 to about 10:1, more preferably from about0.1:1 to about 5:1, and most preferably from 0.4:1 to 0.8:1.

[0021] The aluminum component can exist in the form of anyaluminum-containing compound such as, for example, elemental aluminum,aluminum oxide, and/or an aluminum oxide precursor. Preferably, thealuminum component comprises aluminum oxide. It is preferred for theinventive catalyst composition to contain from about 0.5 to about 25weight percent aluminum based on the total weight of the catalystcomposition, more preferably from about 1 to about 15 weight percentaluminum, and most preferably from 2 to 5 weight percent aluminum. Theweight ratio of aluminum to copper in the inventive catalyst compositionis preferably from about 0.01:1 to about 5:1, more preferably from about0.05:1 to about 1:1, and most preferably from 0.1:1 to 0.2:1.

[0022] The gallium component can exist in the form of anygallium-containing compound such as, for example, elemental gallium,gallium oxide, and/or a gallium oxide precursor. Preferably, the galliumcomponent comprises gallium oxide. It is preferred for the inventivecatalyst composition to contain from about 0.1 to about 15 weightpercent gallium based on the total weight of the inventive catalystcomposition, more preferably from about 0.5 to about 10 weight percentgallium, and most preferably from 1 to 3 weight percent gallium. Theweight ratio of gallium to copper in the inventive catalyst compositionis preferably from about 0.005:1 to about 5:1, more preferably fromabout 0.01:1 to about 1:1, and most preferably from 0.05:1 to 0.2:1.

[0023] The “solid acid” of the inventive composition is defined hereinas being any solid compound which exhibits an acid function (i.e.,functions as a proton donor). Preferably, the solid acid is a zeolite.More preferably, the solid acid is a zeolite having a constraint index(as defined in U.S. Pat. No. 4,097,367, which is incorporated herein byreference) in the range of from about 0.4 to about 12, preferably from 2to 9. Generally, the molar ratio of SiO₂ to Al₂O₃ in the crystallineframework of the preferred solid acid zeolite is about 5:1 and can rangeup to infinity. Preferably, the molar ratio of SiO₂ to A1₂O₃ in thepreferred solid acid zeolite framework is from about 5:1 to about 200:1,more preferably from 40:1 to 70:1. Preferred solid acid zeolites includeZSM-5, ZSM-8, ZSM-11, ZSM-12, ZSM35, ZSM-38, and mixtures thereof. Thepreferred solid acid zeolites can also be described as crystallinealuminosilicates. Suitable aluminosilicates generally have a medium poresize, generally being an effective fine porous size of from about 5 toabout 6.5 angstroms, although small (generally 3 to 5 angstroms) orlarge pore (generally 7 to 8 angstroms) solid acid zeolites can also beused. ZSM-5 and similar solid acid zeolites that have been identified ashaving a framework topology identified as MFI are particularly preferredbecause of their shape selectivity. The presently most preferred solidacid is ZSM-5.

[0024] It is preferred for the inventive catalyst composition to containfrom about 5 to about 80 weight percent solid acid based on the totalweight of the inventive catalyst composition, more preferably from about10 to about 60 weight percent solid acid, and most preferably from 30 to50 weight percent solid acid. The weight ratio of solid acid to copperin the inventive catalyst composition is preferably from about 0.1:1 toabout 20:1, more preferably from about 0.5:1 to about 10:1, and mostpreferably from 1:1 to 2:1.

[0025] The inventive catalyst composition can further comprise a bindercomponent having binding properties which provide for a final catalystcomposition having the desired physical properties. Examples of suitablebinder materials include those selected from the group consisting ofbentonite, aluminate, kaolin, alumina, silica, colloidal silica, sodiumsilicate, titania, zirconia, aluminosilicates (e.g., clays), zincaluminate, zinc titanate, metal oxides, and any mixtures thereof.Preferred binders are selected from the group consisting of bentonite,alumina, silica, aluminosilicates, and any two or more thereof. When theinventive catalyst composition comprises a binder, it is preferred forthe catalyst composition to contain from about 1 to about 40 weightpercent binder based on the total weight of the inventive catalystcomposition, more preferably from about 4 to about 30 weight percentbinder, and most preferably from 8 to 15 weight percent binder. Theweight ratio of binder to copper in the inventive catalyst compositionis preferably from about 0.02:1 to about 10:1, more preferably fromabout 0.1:1 to about 5:1, and most preferably from 0.2:1 to 1:1.

[0026] It is preferred for the copper, zinc, aluminum, and galliumcomponents of the inventive catalyst composition to be present in theform of a coprecipitate with the coprecipitate and the zeolite, andoptionally the binder, being substantially evenly dispersed throughoutthe final catalyst composition.

[0027] In accordance with the second embodiment of the present inventiona method of making the inventive catalyst composition of the firstembodiment of the present invention is provided.

[0028] The inventive catalyst composition is preferably made, at leastin part, by a coprecipitation process. The coprecipitation process canbe commenced by contacting an aqueous metal-salt solution containing acopper compound, a zinc compound, an aluminum compound, a galliumcompound, and water with a basic substance under suitable conditions tocause coprecipitation of the metals. After the solid coprecipitate hasformed, it is allowed to age for a suitable period of time. Thecoprecipitate is then filtered from the remaining liquid solution,washed, dried, and calcined.

[0029] The aqueous metal-salt solution employed in the above-describedcoprecipitation process is preferably formed by combining soluble saltsof copper, zinc, aluminum, and gallium with an appropriate amount of asuitable solvent. The soluble salts of copper, zinc, aluminum, andgallium can be, for example, nitrates, acetates, halides, or any othersuitable salts known to those skilled in the art to form the desiredproduct. Most preferably, the metal-salt solution is formed by combiningcopper nitrate, zinc nitrate, aluminum nitrate, gallium nitrate, andwater in appropriate amounts. Preferably, the ratio of zinc to copper inthe aqueous metal-salt solution is from about 0.01:1 to about 10:1, morepreferably from about 0.1:1 to about 5:1, and most preferably from 0.4:1to 1:1. Preferably, the weight ratio of aluminum to copper in theaqueous metal-salt solution is from about 0.01:1 to about 5:1, morepreferably from about 0.05:1 to about 1:1, and most preferably 0.1:1 to0.2:1. Preferably, the weight ratio of gallium to copper in the aqueousmetal-salt solution is from about 0.005:1 to about 5:1, more preferablyfrom about 0.01:1 to about 1:1, and most preferably from 0.05:1 to0.2:1. The amount of solvent, preferably water, employed in the solutioncan be any amount of solvent sufficient to dissolve the metal salts.Preferably, the weight ratio of solvent to the copper in the aqueousmetal-salt solution is from about 0.1:1 to about 1,000:1, morepreferably from about 1:1 to about 100:1, and most preferably from 5:1to 20:1.

[0030] The basic substance contacted with the aqueous metal-saltsolution can be any substance operable to facilitate coprecipitation ofa Cu/Zn/Al/Ga solid coprecipitate. The basic substance is preferably aliquid substance having a pH value of more than about 8, preferablybetween about 9 and 12. The basic substance preferably comprises a basiccomponent selected from the group consisting of ammonia, carbonates,bicarbonates, and alkali metal hydroxides. Most preferably, the basicsubstance is an aqueous solution containing sodium bicarbonate andwater, with the weight ratio of sodium bicarbonate to water in thesolution being from about 0.01:1 to 10:1, most preferably from 0.05:1 to0.2:1.

[0031] The aqueous metal-salt solution is preferably contacted with thebasic solution by combining the basic substance and the metal-saltsolution in a mixer. Preferably, after combining the basic substance andthe metal-salt solution, the resulting solution is mixed by any suitablemethod known in the art for a period of about 5 minutes to about 5hours, more preferably from about 10 minutes to about 1 hour. Duringmixing of the metal-salt solution and the basic substance, it ispreferred that the mixed solution be maintained at a temperature of fromabout 10° C. to about 200° C., more preferably from about 20° C. toabout 100° C., and most preferably from about 60° C. to about 80° C.

[0032] After mixing, the formed coprecipitate and liquid solution arepreferably aged, without mixing, at a temperature of from about 20° C.to about 100° C. for a time period of from about 10 minutes to about 5hours.

[0033] The solid coprecipitate formed during the mixing and aging of thesolution is preferably separated from the liquid solution by any meansknown in the art such as, for example, filtering. The separated solidcoprecipitate is then preferably washed to remove trace amounts of theliquid solution therefrom. After washing, the solid coprecipitate ispreferably dried at a temperature of from about 80° C. to about 200° C.,more preferably from 100° C. to 140° C. for a period of from about 0.5to about 10 hours, more preferably from about 1 to about 5 hours.Thereafter, the dried solid coprecipitate is preferably calcined at atemperature of from about 200° C. to about 600° C., more preferably fromabout 300° C. to about 400° C. for a period of from about 1 to about 20hours, more preferably from about 2 to about 8 hours.

[0034] The calcined coprecipitate comprising copper, zinc, aluminum, andgallium is thereafter preferably physically mixed with the solid acidand the binder in appropriate proportions suitable for providing theinventive catalyst composition described in the first embodiment of thepresent invention. The solid coprecipitate is preferably crushed intofine particles prior to or during mixing with the solid acid and binder.Water can be added during the physical mixing of the solidcoprecipitate, solid acid catalyst, and binder to thereby form a pastecapable of being shaped into suitable catalyst particles. Preferably,the paste is thereafter extruded into extrudate having a diameter offrom about {fraction (1/16)} to about ⅛ of an inch. Other suitablemethods of shaping such as, for example, granulizing, pelletizing, andsphering may also be employed.

[0035] After shaping the mixture of solid coprecipitate, solid acid, andbinder, the shaped catalyst is preferably dried at a temperature of fromabout 80° C. to about 200° C. for a period of from about 1 to about 10hours. The dried catalyst is then calcined at a temperature of fromabout 200° C. to about 600° C., preferably from 300° C. to 400° C., fora period of from about 1 to about 10 hours, preferably from 3 to 7hours.

[0036] After calcining, the catalyst is preferably reduced underconditions sufficient to reduce the valence of the copper component ofthe catalyst. Preferably, reduction is accomplished by contacting thecatalyst with hydrogen at a temperature of from about 180° C. to about320° C., preferably from 200° C. to 280° C., for a period of from about0.5 to about 20 hours, preferably from 2 to 8 hours.

[0037] In accordance with a third embodiment of the present invention aprocess for converting carbon dioxide to oxygenates using the inventivecatalyst composition described in the first embodiment of the presentinvention is provided.

[0038] The catalyst described and prepared in accordance with the firstand second embodiments of the present invention can be employed toconvert a feed containing carbon dioxide into oxygenates under anysuitable conditions effective to promote such conversion. The carbondioxide-containing feed and catalyst can be contacted in the reactionzone of any suitable reactor known in the art such as, for example, afixed bed reactor, a moving bed reactor, a fluidized bed reactor, andtransport reactors. Preferably, the inventive catalyst and the carbondioxide-containing feed are contacted in a fixed bed reactor.

[0039] The carbon dioxide-containing feed contacted with the inventivecatalyst composition preferably comprises hydrogen and carbon dioxide inamounts such that the hydrogen to carbon dioxide volume ratio (H₂:CO₂)of the feed is in the range of from about 0.1:1 to about 100:1, morepreferably from about 1:1 to about 50:1, and most preferably from 5:1 to15:1. Although the carbon dioxide-containing feed can contain traceamounts of other compounds such as, for example, carbon monoxide, it ispreferred that the carbon dioxide-containing feed consist essentially ofhydrogen and carbon dioxide. Preferably, the volume percent of carbondioxide in the carbon dioxide-containing feed is from about 1 to about50 volume percent by volume of the total carbon dioxide-containing feed,more preferably from about 5 to about 20 volume percent, and mostpreferably from 8 to 15 volume percent. The volume of hydrogen containedin the carbon dioxide-containing feed is preferably from about 50 toabout 99 volume percent hydrogen based on the total volume of the carbondioxide-containing feed, more preferably from about 70 to about 95volume percent hydrogen, and most preferably from 85 to 95 volumepercent hydrogen.

[0040] The carbon dioxide-containing feed preferably comprises less thanabout 20 volume percent of compounds other than carbon dioxide andhydrogen based on the total volume of the carbon dioxide-containingfeed, more preferably less than about 10 volume percent of compoundsother than carbon dioxide and hydrogen, even more preferably less than 2volume percent of compounds other than carbon dioxide and hydrogen.

[0041] The rate at which the carbon dioxide-containing feed is chargedto the reactor can be any rate suitable for promoting the conversion ofcarbon dioxide to oxygenates, particularly dimethyl ether. Preferably,the gas hourly space velocity (GHSV) of the carbon dioxide-containingfeed charged to the reactor is in the range of from about 100 to about20,000 hr⁻¹, more preferably from 1,000 to 5,000 hr⁻¹.

[0042] The temperature and pressure at which the reaction zone of thereactor is maintained can be any temperature and pressure whichoptimizes the conversion of carbon dioxide to oxygenates, particularlydimethyl ether. The reaction zone is preferably maintained at atemperature of from about 150° C. to about 500° C., more preferably fromabout 200° C. to about 400° C., and most preferably from 250° C. to 320°C. The pressure in the reaction zone is preferably from about 200 psigto about 5,000 psig, more preferably from about 500 psig to about 4,000psig, and most preferably from 1,200 psig to 1,600 psig.

[0043] After contacting the carbon dioxide-containing feed and thecatalyst composition under reaction conditions, the oxygenate productscan be recovered from the reactor by any suitable means known in theart.

[0044] The product of the reaction preferably comprises dimethyl ether(DME), methanol, and carbon monoxide. The amount of DME in the productas a mole percentage of all the carbon in the product is preferablygreater than about 5 carbon mole percent, more preferably greater thanabout 20 carbon mole percent, and most preferably greater than 60 carbonmole percent. The amount of methanol in the product as a mole percentageof all the carbon in the product is preferably less than about 50 carbonmole percent, most preferably less than 25 carbon mole percent. Theamount of carbon monoxide in the product as a mole percentage of all thecarbon in the product is preferably less than about 20 carbon molepercent, more preferably less than about 10 carbon mole percent, andmost preferably less than 5 carbon mole percent.

EXAMPLE I

[0045] Catalyst A (control) was prepared by combining 22.0 grams ofcopper nitrate (Cu(NO₃)₂.2±2H₂O), 14.07 grams of zinc nitrate(Zn(NO₃)₂.6H₂O), 2.95 grams of aluminum nitrate (Al(NO₃)₂.9H₂O), 2.16grams of gallium nitrate (Ga (NO₃)₂.H₂O), and 200 ml of water to form ametal-salt solution. A basic solution containing 20 grams of sodiumcarbonate (Na₂CO₃) and 200 ml of water was prepared separately. Themetal-salt solution and the basic solution were then simultaneouslyadded to a mixer containing 100 ml of water at 70° C. over a period ofabout 30 minutes while the mixer was agitating. The mixer was thenturned off and its contents were allowed to age at 70° C. for about 1hour. The solid coprecipitate substance formed in the mixer was thenfiltered from the liquid contents of the mixer and washed with water.The washed coprecipitate was placed in an oven and dried at 120° C. forabout 3 hours. The dried coprecipitate was then calcined by raising theoven temperature to 350° C. for about 5 hours. The resulting 11.90 gramquantity of the calcined coprecipitate was designated Coprecipitate X.

[0046] A 3.0 gram quantity of Coprecipitate X was then crushed into apowder and mixed with 0.3 grams of bentonite. Water was slowly added tothe mixture during mixing to form a paste. The paste was extruded with asyringe into extrudate having a diameter of approximately {fraction(1/16)} inch. The extrudate was placed in an oven and dried at 120° C.for about 3 hours. The dried extrudate was then calcined by raising theoven temperature to 350° C. for 3 hours. The resulting calcinedextrudate was designated Catalyst A.

[0047] Catalyst B (inventive) was prepared by mixing a 5.95 gramquantity of Coprecipitate X, described above, a 5 gram quantity of ZSM-5zeolite (Zeocat PZ2/50H powder, provided by CU Chemie Uetikon AG,Uetikon, Switzerland), and a 1.5 gram quantity of bentonite. An 11.5 mlquantity of water was slowly added to the mixture during mixing to forma paste. The paste was then extruded, dried, and calcined in the samemanner as described above with respect to the preparation of Catalyst A.The resulting calcined extrudate was designated Catalyst B.

EXAMPLE II

[0048] Catalyst A (control) was reactor tested by placing 2.5 grams ofCatalyst A in a stainless steel tube reactor (I.D.=1 cm; length=60 cm).Catalyst A was reduced by charging hydrogen at about 50 cc/min to thereactor while maintaining the reactor at a temperature of about 240° C.After reduction, a feed of carbon dioxide and hydrogen having a H₂/CO₂volume ratio of 9 was charged to the reactor at a GHSV of 2650 hr⁻¹while the reactor was maintained at a temperature of 280° C. and apressure of 1400 psig. Effluent samples were taken in 5 increments overa period of about 4.5 hours.

[0049] Catalyst B (inventive) was reactor tested by placing 4.75 gramsof Catalyst B in the same reactor as was used to test Catalyst B.Catalyst B was then reduced and reacted with the same H₂/CO₂ feedemployed for Catalyst A in substantially the same manner as describedabove with respect to Catalyst A. Effluent samples were taken at 6increments over a period of about 6.5 hours.

[0050] The effluent samples from the reactor tests of Catalysts A and Bwere analyzed by gas chromatograph to determine average CO₂ conversion(%) and product selectivity (carbon mole %) to CO, methanol, anddimethyl ether. TABLE 1 CO₂ Product Selectivity (Carbon mole %) CatalystConversion (%) CO Methanol Dimethyl Ether A 56.6 16.0 83.2 0.2 B 72.14.6 20.1 75.0

[0051] Table 1 illustrates that a Cu/Zn/Al/Ga catalyst including a solidacid component (Catalyst B) provides superior CO₂ conversion anddimethyl ether selectivity versus a Cu/Zn/Al/Ga catalyst that does notinclude a solid acid component (Catalyst A).

[0052] Reasonable variations, modifications, and adaptations can be madewithin the scope of this disclosure and the appended claims withoutdeparting from the scope of this invention.

[0053] The inventors hereby state their intent to rely on the Doctrineof Equivalents to determine and assess the reasonably fair scope of thepresent invention as pertains to any apparatus not materially departingfrom but outside the literal scope of the invention as set forth in thefollowing claims.

What is claimed is:
 1. A process for converting a carbondioxide-containing feed into oxygenates, said process comprising thesteps of: (a) contacting said carbon dioxide-containing feed with acatalyst composition comprising copper, zinc, aluminum, gallium, and asolid acid in a reaction zone under reaction conditions sufficient toconvert at least a portion of said carbon dioxide-containing feed intooxygenates; and (b) recovering at least a portion of said oxygenatesfrom said reaction zone.
 2. A process according to claim 1, said carbondioxide-containing feed further comprising hydrogen.
 3. A processaccording to claim 2, said carbon dioxide-containing feed comprisingsaid hydrogen and said carbon dioxide in amounts such that the volumeratio of said hydrogen to said carbon dioxide of said feed is in therange of from about 0.1:1 to about 100:1.
 4. A process according toclaim 3, said carbon dioxide-containing feed comprising said carbondioxide in an amount in the range of from about 1 to about 50 volumepercent by volume of the total carbon dioxide-containing feed.
 5. Aprocess according to claim 4, said carbon dioxide-containing feedcomprising said hydrogen in an amount in the range of from about 50 toabout 99 volume percent by volume of the total carbon dioxide-containingfeed.
 6. A process according to claim 5, said carbon dioxide-containingfeed comprising compounds other than carbon dioxide and hydrogen in anamount which is less than about 20 volume percent by volume of the totalcarbon dioxide-containing feed
 7. A process according to claim 1, saidsolid acid comprising a zeolite.
 8. A process according to claim 1, saidsolid acid comprising ZSM-5.
 9. A process according to claim 1, saidreaction conditions including a temperature of from about 50° C. toabout 500° C. and a pressure of from about 200 psig to about 5,000 psig.10. A process according to claim 1, said carbon dioxide-containing feedbeing charged to said reaction zone at a GHSV of from about 100 to about20,000 hr⁻¹.
 11. A process according to claim 1, said carbondioxide-containing feed consisting essentially of carbon dioxide andhydrogen.
 12. A process for converting a carbon dioxide-containing feedstream into oxygenates, said process comprising the steps of: (a)contacting said feed stream with a catalyst composition comprisinggallium in a reaction zone under reaction conditions sufficient toconvert at least a portion of said feed stream into oxygenates, saidfeed stream comprising carbon dioxide and hydrogen in a volume ratio ofabout 0.1:1 to about 100:1, and said feed stream comprising less thanabout 20 volume percent of components other than hydrogen and carbondioxide; and (b) recovering at least a portion of said oxygenates fromsaid reaction zone.
 13. A process according to claim 12, said feedstream comprising carbon dioxide and hydrogen in a volume ratio of about1:1 to about 50:1.
 14. A process according to claim 12, said feed streamcomprising carbon dioxide and hydrogen in a volume ratio of 5:1 to 15:1.15. A process according to claim 12, said feed stream comprising lessthan about 10 volume percent of components other than carbon dioxide andhydrogen.
 16. A process according to claim 12, said feed streamcomprising less than 2 volume percent of components other than carbondioxide and hydrogen.
 17. A process according to claim 12, said feedstream consisting essentially of carbon dioxide and hydrogen.
 18. Aprocess according to claim 12, step (a) including reacting carbondioxide with hydrogen to thereby produce said oxygenates.
 19. A processaccording to claim 12, said oxygenates comprising dimethyl ether.
 20. Aprocess according to claim 12, said catalyst composition comprising asolid acid.
 21. A process according to claim 20, said catalystcomposition comprising copper.
 22. A process according to claim 21, saidcatalyst composition comprising zinc.
 23. A process according to claim22, said catalyst composition comprising aluminum.
 24. A process forconverting a carbon dioxide-containing feed into oxygenates, saidprocess comprising the steps of: (a) contacting said carbondioxide-containing feed with a catalyst composition comprising galliumin a reaction zone under reaction conditions sufficient to convert atleast a portion of said feed stream into a product stream comprisingdimethyl ether. (b) recovering at least a portion of said dimethyl etherfrom said reaction zone.
 25. A process according to claim 24, saidcarbon dioxide-containing feed comprising at least about 80 volumepercent carbon dioxide and hydrogen, said product stream comprising atleast about 20 carbon mole percent dimethyl ether.
 26. A processaccording to claim 25, said product stream comprising less than about 50carbon mole percent methanol.
 27. A process according to claim 24, saidcarbon dioxide containing feed comprising at least 98 volume percentcarbon dioxide and hydrogen, said product stream comprising at least 60carbon mole percent dimethyl ether.
 28. A process according to claim 27,said product stream comprising less than 25 carbon mole percentmethanol.
 29. A process according to claim 24, said carbondioxide-containing feed consisting essentially of carbon dioxide andhydrogen.
 30. A process according to claim 24, step (a) includingconverting carbon dioxide into said dimethyl ether.
 31. A processaccording to claim 24, said catalyst composition comprising a solidacid.
 32. A process according to claim 31, said catalyst compositioncomprising copper.
 33. A process according to claim 32, said catalystcomposition comprising zinc.
 34. A process according to claim 33, saidcatalyst composition comprising aluminum.
 35. A process for converting acarbon dioxide-containing feed into oxygenates, said process comprisingthe steps of: (a) contacting said carbon dioxide-containing feed with acatalyst composition comprising a solid acid in a reaction zone underreaction conditions sufficient to convert at least a portion of saidfeed stream into oxygenates, said carbon dioxide-containing feedcomprising at least 90 volume percent carbon dioxide and hydrogen; and(b) recovering at least a portion of said oxygenates from said reactionzone.
 36. A process according to claim 35, said catalyst compositioncomprising gallium.
 37. A process according to claim 35, said carbondioxide-containing feed comprising at least 98 volume percent carbondioxide and hydrogen.
 38. A process according to claim 37, said catalystcomposition comprising gallium and copper.
 39. A process according toclaim 35, said carbon dioxide-containing feed consisting essentially ofcarbon dioxide and hydrogen.
 40. A process according to claim 39, saidcatalyst composition comprising gallium, copper, zinc, and aluminum. 41.A process according to claim 35, said feed comprising carbon dioxide andhydrogen in a volume ratio of about 1:1 to about 50:1.
 42. A processaccording to claim 35, said oxygenates comprising dimethyl ether.